How many WMers are there in Canada?  And how do we know?

The “urban myth” says “oh, there are about 150 people diagnosed with WM in Canada every year”.  But for some of us, this wasn’t enough.  We wanted to know.  And it just wasn’t enough to refer to the urban myth.

The obvious place to look is, perhaps, the Canadian Cancer Society (the CCS).  They publish an annual report containing extensive statistics on cancer in Canada.  The latest one, for 2021, is an excellent reference.  Unfortunately, while the CCS does a great job breaking down the various types of cancer, they do not go down to the level of detail that we need.  They get down to “Non-Hodgkin Lymphoma”, and that’s it.  Now, there are statistics in this report that we can use (see below), but only if we have other statistics available to us.

After much searching and discussion, we converged on two published, peer-reviewed papers:

  1. does some statistical analysis on reported diagnoses of WM in the US (note these are diagnoses, not necessarily verified cases using uniform diagnostic parameters); and
  2. does a decades-long analysis of the frequency of WM cases in the county in which the Mayo clinic resides (Olmsted County, Minnesota), thus providing numbers that are quite exact, using uniform diagnostic parameters.  We say “exact” because they work within a tight geographic focus, and they are one of the expert sites for WM

Paper #1 reported that WM was diagnosed in 1.9% of Non-Hodgkins Lymphoma (NHL) diagnoses in the US in the timeframe and geographies in the SEER database.  Assuming Canadian and US diagnosticians are of equal skill, and that the underlying rate of WM is the same in both countries, then we can do some math:  the Canadian Cancer Society reported 257 NHL cases per million in 2021; at 1.9%, that would be 4.9 WM diagnoses per million population per year.

As a different measure, paper #1 also reported 3.8 WM diagnoses per million as the age-adjusted incidence rate, with wide variation over age, and significant error bars.

Paper #2 reported 5.7 WM cases per million, steady over time, over the 50 years in which they had statistics.  This number also has fairly large error bars.  And we’ll assume (below) that the incidence rate of WM in Canada is roughly the same as the incidence rate in Olmsted County, Minnesota — remember, the error bars are large.

And lastly, let’s assume that we can ignore the distinction between verified cases and proposed diagnoses.  It really doesn’t matter to the patient when they first hear the words “Waldenstrom’s Macroglobulinemia” coming from their doctor.

Then we can say the following:  The Stats Canada population of Canada was 38 million in 2020.  The various rates given above would give us:

  • @3.8 per million: 144 new patients per year
  • @4.9 per million: 186 new patients per year
  • @5.7 per million: 216 new patients per year

Given the large error bars in all of the numbers, the precise number is not the issue.  Their magnitude, though, indicates that there are somewhere between, say, 120 and 220 new WM patients per year in Canada.

So … on a last note … where are all of these new WMers?  Surely they should be getting in touch with us and joining!  If you have suggestions as to how we can find all of these WMers and make sure they know we exist, get in touch with us!

(Ed. note:  And if at this point you’re going to say, “Hey, you never answered the question at the top — you’ve said how many new WMers per year, but not how many there are in Canada, today, in total!”, you’re absolutely right!  Because that’s really difficult.  We know that, as a result of research and modern treatments, people with WM are living longer.  But going from this rate (with large error bars) to a total number of WMers alive in Canada right now (again, with large error bars) is a really difficult problem in statistics.  If you’d like to take a go at it, contact us!)